We have dissociated myocardial muscle cells from newborn rats and from adult rats and rabbits. These preparations are being used to study the contractile, electrophysiological, and biochemical characteristics in a variety of different conditions. In particular we have been able to identify in these isolated cells a longitudinally propagating wave which occurs spontaneoulsy when the cell is not being electrically stimulated and is considered at rest and has a normal resting membrane potential. These "waves" are likely to represent the phenomenon of calcium induced calcium release and are the cause of the scattered light intensity fluctuations (SLIF) which our laboratory has studied in the past in multicellular preparations. These conclusions are drawn by the fact that SLIF and the "waves" respond in the same way to changes in the extracellular calcium or sodium and to the addition of caffeine to the medium.